1. Field of the Invention
This invention relates to an emulsion composition for use in a baking paint having high water resistance, solvent resistance, chemical resistance and weatherability and having good gloss and physical properties. More particularly, this invention relates to an emulsion composition, for use in a baking paint, which is prepared by emulsion polymerization of a monomer mixture comprising a specified acrylamide, a radical polymerizable ethylenic unsaturated monomer having a hydroxyl group, and another radical polymerizable ethylenic unsaturated monomer. The resulting emulsion can be used in a baking paint or enamel which is coated on a substrate and heated for curing.
2. Description of the Prior Art
With the current concern over air pollution and depletion of natural resources, the social demand has increased for the development of an innovative technology for making substitutes for the resin composition using an organic solvent as a medium, and one of such substrates is a polymer emulsion using water as a medium. Heretofore, various emulsions that meet specific purposes have been developed and used as paints. These emulsions are prepared by thermal emulsion polymerization that unavoidably uses a radical polymerization initiator and other water soluble compounds that will form a great amount of low-molecular hydrophilic resins. As a result, the paint film is poor in water resistance, solvent resistance, chemical resistance, gloss, weatherability and physical properties. To eliminate these disadvantages, it was previously proposed to use ionizing radiation to prepare an aqueous emulsion for use in a baking paint (see Japanese patent application Nos. 53329/77 to 53333/77). The basic concept of these processes was to prepare an emulsion having a hydroxyl group as a functional group, which was usually mixed with a melamine resin before thermal curing thereof. However, because the proposed emulsions must have miscibility with the melamine resin used as a crosslinking agent, only a few compositions could be selected for the emulsion, and in addition, a slight amount of melamine resin exuded to the surface of the film and made the film look dull.